The present invention is a method and apparatus for the calculation of coal ash fusion values based upon the measurement of predetermined ash fusion values.
The efficient operation of coal-fired power plant boilers and other boilers and furnaces with a minimum of slagging and fouling problems depends on the determination of accurate ash fusion temperatures for the coals used as fuels. Such industrial combustion equipment may remove the byproducts of the combustion process in either a solid or liquid form depending on equipment type. It is imperative that the coal utilized maintain appropriate ash properties during the entire handling process. Ash fusion temperatures are a useful guide to a coal's expected behavior.
Before coal or coke is burned in a furnace, the fuel is analyzed to determine the fusibility of the coal or coke ash. Burning coal or coke in a commercial steel mill furnace, which generates temperatures sufficiently high to fuse the ash, causes the ash to collect on various furnace components, most notably the furnace grates. If collection becomes excessive, the furnace must be shut down, cooled, and cleaned, requiring costly excessive periods of furnace inactivity. By selecting coal with desired properties, such problems can be minimized.
The ASTM standard test method for determining the fusibility of coal and coke ash requires the prepared ash to be formed into triangular, generally pyramid-shaped cones which are placed within an analytical furnace. The temperature within the furnace is then increasingly ramped at 15° F. per minute, and the cones are manually observed to detect changes in shape. The fusibility of the ash is recorded at four temperatures; namely, (1) the temperature at which the apex of the cone becomes rounded known as initial deformation temperature (IDT, hereinafter abbreviated as IT); (2) the temperature at which the height of the deformed cone is equal to the width of the base known as the softening temperature (ST); (3) the temperature at which the height of the deformed cone is equal to one-half the width of the base known as the hemispherical temperature (HT); and, finally, (4) the temperature at which the cone has been reduced to a lump having a height no greater than one-sixteenth inch known as the fluid temperature (FT).
This test method has several significant drawbacks. First the method is time-consuming and requires an observer to constantly monitor all cones within the furnace as all cones pass through all four stages of fusion. This task is tedious and the observer can become inattentive, resulting in inaccurate temperature readings. Second, monitoring the shape of five cones (the typical furnace load) is difficult. Third, the findings are somewhat subject to the individual judgment of the human observer, further introducing error and/or variation into the test results. The ASTM test method recognizes these problems and provides for relatively large acceptable errors in excess of 50° C. or 100° F. for each of the four stages of fusion.
Improvements in ash fusion determinators have greatly improved the accuracy of the determination of IT, ST, HT, and FT. An ash fusion determinator Model No. AF700, commercially available from Leco Corporation of St. Joseph, Mich., represents state-of-the-art advances over several earlier determinators, such as disclosed in U.S. Pat. Nos. 4,462,963 and 4,522,787. The AF700 ash fusibility determinator automatically monitors ash cone deformation temperatures in coal ash, coke ash, and mold powders. Prepared ash cones are mounted on a ceramic tray and placed into a high-temperature, rampable furnace. The user selects an analytical method with a predefined furnace atmosphere (oxidizing or reducing) and a ramp rate (° C./minute) for the furnace based on approved methodologies. The furnace is first purged with nitrogen before the selected atmosphere is introduced. A high-resolution digital camera collects images (up to 30 frames/minute) after the furnace temperature reaches the method-defined starting point (typically 1382° F./750° C.). Predefined ash fusibility temperatures (IT, ST, HT, and FT) may be automatically determined using Image Recognition Functions (IRF) within the software. In addition, IRF allows the analysis to be automatically terminated after all deformation points have been reached for all samples, increasing throughput and furnace lifetime. Alternately, the furnace can be programmed to cycle between the method-defined starting temperature (e.g. 752° F./400° C.) and a maximum programmed furnace temperature (typically 2730° F./1500° C. and a maximum of 2900° F./1600° C.). A complete image history for all analyzed samples is digitally archived for easy retrieval and review on DVD, CDRW, or hard drive. Archived images may be used to make subjective determinations of deformation temperatures.
Although such a determinator has greatly improved the efficiency of the determination of the ash fusion temperature, subjective, somewhat error-prone steps, are still required. Although the softening temperature (ST) and hemispherical temperature (HT) phases are well defined in mathematical terms, the initial deformation temperature (IDT or IT) and the fluid temperature (FT) phases remain subjective observations and are much more difficult to accurately determine. Thus, there remains a need for improvement in the accurate determination of the ASTM ash fusion temperatures.